diff --git a/src/clock.c b/src/clock.c
index 191525411a6610539d9c365557c344521f21bc16..7df13775b29092e78e988bb8e2adb915f4935464 100644
--- a/src/clock.c
+++ b/src/clock.c
@@ -23,7 +23,7 @@
 #ifdef RT_USING_SMP
 #define rt_tick rt_cpu_index(0)->tick
 #else
-static rt_tick_t rt_tick = 0;
+static volatile rt_tick_t rt_tick = 0;
 #endif
 
 /**